Filters of filter cigarettes each have a rod-like filter material and a wrapping material in which the filter material is wrapped. There is a filter having apertures in its wrapping material. When a filter cigarette having a filter with apertures is smoked, air flows into the filter through these apertures, and smoke from the cigarette is therefore diluted. This reduces nicotine and tar contained in the smoke, so that the smoker can enjoy a light flavor.
The ratio of the amount of air that flows in through the apertures to the amount of smoke that the smoker draws in is called filter ventilation (hereinafter, also simply referred to as VF). Unless the filter cigarettes individually have fixed VF, their flavor is not steady, which causes quality variation.
The International Organization for Standardization defines a method of measuring the VF. Unexamined Japanese Patent Application Publication No. 2000-39392 discloses a ventilation inspecting apparatus that is employed for this measuring method. The ventilation inspecting apparatus has a plurality of thin packings and suction means. Each of the packings axially partitions the inside of a measuring hole into which a filter cigarette is inserted.
In the center of each packing, there is formed a seal hole with a diameter that is slightly smaller than the external diameter of a filter cigarette. The diameter of the seal hole is expandable. When the filter cigarette is inserted into the measuring hole, the suction means sucks the outer edge of the packing to expand the seal hole, and allows the filter cigarette to pass through the seal hole. At the time of ventilation measurement, the sucking by the suction means is cancelled, so that the seal hole grows small in diameter. The inner circumferential edge of the seal hole is brought into airtight contact with the outer circumferential surface of the filter cigarette.
Once the inner circumferential edge of the seal hole is brought into tight contact with the filter cigarette, first and second chambers are formed in the measuring hole. The filter portion of the filter cigarette is inserted into the first chamber. The end of the filter portion of the filter cigarette is protruding a little into the second chamber. The first and second chambers communicate with each other through the inside of the filter portion.
According to the ventilation inspecting apparatus, while the flow rate of test gas flowing into the first chamber is measured, the test gas is sucked from the second chamber at a predetermined flow rate. Based upon the ratio of these flow rates, filter ventilation is calculated.
However, the packings of the ventilation inspecting apparatus disclosed in the above document are thin, and the diameters of their seal holes are expanded by a sucking force, so that the packings are poor in durability. As a result, the airtightness of the first and second chambers to be separated by the packing is liable to decrease, which widens the measurement error of the VF. Especially, if the airtightness of the packing between the first and second chambers is degraded, part of the test gas supplied into the first chamber directly flows into the second chamber without flowing through the inside of the filter portion. This widens the measurement error of the VF to a considerable degree. Consequently, nicotine and tar amounts in the filter cigarette cannot be reliably controlled.
The ventilation inspecting apparatus disclosed in the above document is used to carry out a sampling inspection of the VF of some of the manufactured filer cigarettes. This is because the inspecting apparatus is difficult to be installed into a cigarette manufacturing machine due to its structure. Even if the inspecting apparatus can be installed into the cigarette manufacturing machine, the apparatus is not suitable to inspect the VF of all the manufactured filter cigarettes because of the low durability of the packings.